The present invention generally relates to the blood dialysis and, more particularly, to a method for the blood dialysis and an apparatus utilizing a dialyzer for the removal of waste products of metabolism from the blood. The method and apparatus herein disclosed according to the present invention are aimed at maximizing the utilization of a dialyzing solution thereby to minimize the consumption of the dialyzing solution.
A technique of blood dialysis by the use of a dialyzer, or an artificial kidney as it is generally known, has long been widely practised to purify the human blood by the removal of waste products of metabolism in the body of a patient suffering from a kidney failure. In this case, the dialyzer functions in lieu of the kidney then failing to function properly.
FIG. 1 of the accompanying drawings illustrate schematically an extracorporeal blood circuit extending from an artery to a vein, for example, from a radial artery to a saphenous vein of a patient A, in which circuit the prior art dialyzing apparatus is placed. The extracorporeal blood circuit shown therein includes an inlet cannula la, inserted into the radial artery, and an outlet cannula lb inserted into the saphenous vein. According to the prior art, the blood to be dialyzed and flowing into the inlet cannula la is pumped by a blood pump 2 so as to flow towards a dialyzer unit 3 through a tubing 5a and then towards the outlet cannula lb through a tubing 5 after having passed through a blood chamber in the dialyzer unit 3. The blood so flowing to the outlet cannula lb after waste products of metabolism have been removed therefrom is eventually returned to the saphenous vein of the patient A. In addition to the blood chamber, the dialyzer unit 3 has a dialysate chamber communicated through a solution inlet 8a to a source of dialyzing solution on the one hand and through a dialysate outlet 8b to any suitable dialysate disposing container on the other hand. In order to achieve the positive ultrafiltration, that is, in order to create a pressure difference between the flow of the blood within the blood chamber and that of the dialyzing solution within the dialysate chamber to enable the waste products of metabolism contained in the blood to be forced into the dialyzing solution through a membrane within the dialyzer unit 3, the tubing 5 on the downstream side with respect to the direction of flow of the blood towards the outlet cannula lb has a flow regulator 4 for adjustably constricting the tubing 5. For monitoring the ultrafiltration pressure, a portion of the tubing 5a between the pump 2 and the dialyzer unit 3 and a portion of the tubing 5 between the dialyzer unit 3 and the flow regulator 4 have respective air traps 6a and 6b disposed thereon and fluid-connected with associated pressure gauges 7a and 7b.
When in use for the blood dialysis, the blood pump 2 is operated to effect the extracorporeal circulation of the blood through the extracorporeal blood circuit by way of the dialyzer unit 3 while the flow regulator 4 is adjusted in the light of the readings given by the pressure gauges 7a and 7b to create a proper positive ultrafiltration pressure.
During the blood dialysis so performed, the movement of substances and water by the effect of the osmotic pressure as well as the movement of water by the effect of the ultrafiltration take place within the dialyzer unit. Considering that the water is a substance, it is well known that the movement of the substances within the dialyzer unit has the following relationship: ##EQU1##
According to this notion, the velocity of movement of the substances is proportional to the gradient of concentration, but inversely proportional to the resistance to the fluid flow. The resistance to the fluidflow includes not only that given by the semipermeable membrane, which divides the interior of the dialyzer unit into the blood chamber and the dialysate chamber, but also that given by the interlayer of fluid present between one of the opposite surfaces of the semipermeable membrane and the flow of blood within the blood chamber and between the other of the opposite surfaces of the semipermeable membrane and the flow of dialysate within the dialysate chamber. FIG. 2 illustrates an explanatory diagram showing the concentration gradient and the fluid interlayer on each side of the semipermeable membrane. Assuming that the concentration of a certain substance in the blood and that in the dialysate are expressed by C.sub.B and C.sub.D, respectively, and the coefficent of mobility of the substances as a whole is expressed by K, the velocity N.sub.A of movement of the substances per unit surface area of the semipermeable membrane can be expressed as follows: EQU N.sub.A =K(C.sub.B -C.sub.D)
Also, it is well known that, assuming that the coefficient of mobility of the substances across the fluid interlayer on the side of the blood chamber and that on the side of the dialysate chamber are expressed by K.sub.B and K.sub.D, respectively, the coefficient of diffusion of the substances in the semipermeable membrane is expressed by D.sub.H, and the thickness of the semipermeable membrane is expressed by L, the resistance 1/K as a whole is equal to the sum of the resistances given by the fluid interlayer confronting the blood chamber, the semipermeable membrane and the fluid interlayer confronting the dialysate chamber, that is, the following relationship can be established (The Journal of the Society of Reserch on Artificial Dialysis, Vol. 2 No. 2, 1969, p98 et seqq.): ##EQU2##
Accordingly, it can be deduced that, for a dialyzer unit of given design to exhibit an increased dialyzing efficiency, the rate of flow of both of the blood and the dialysate has to be increased to induce a turbulence adjacent the respective surfaces of the semipermeable membrane thereby to reduce the resistances. However, so far as the rate of flow of the dialysate is concerned, the increase of the flow rate to a value as high as permissible may result in the increase of the dialyzing efficiency, which in turn results in the increased consumption of the dialyzing solution. In view of this, in consideration of numerous factors such as the dialyzing efficiency, the dialyzing time and the consumption of the dialyzing solution, the compromise has hitherto been made to supply the dialyzing solution continuously through the dialysate chamber at a rate of about 50 ml/min. Where a plurality of dialyzer units are used, the current practice is either to employ a dialyzing solution supply system for each of the dialyzer units or to employ a large volume dialyzing solution supply system for all of the dialyzer units and, in either case, the total quantity of the dialyzing solution required to be continuously supplied to the dialyzer units amounts to a multiple of the quantity required for each dialyzer unit.
In the conventional method and apparatus for the dialysis, the dialyzing solution is continuously supplied through the solution inlet 8a into the dialysate chamber at which the dialyzing solution is mixed with the substances filtered from the blood chamber through the semipermeable membrane. The dialyzing solution so mixed with the substance, i.e., the waste products of metabolism from the blood, is then discharged continuously as the dialysate from the dialysate outlet 8b. Since a relatively great quantity of the dialyzing solution is accordingly consumed, the conventional method and apparatus require the use of a correspondingly great quantity of both pure water and an undiluted dialyzing liquid to be mixed with the pure water to provide the dialyzing solution. In addition, the heating of the dialyzing solution to a required temperature results in the consumption of a relatively great amount of electric power because of the use of the great quantity of the solution. These disadvantages necessitate the use of a relatively complicated, bulky and expensive device for the preparation and supply of the dialyzing solution.
Apart from the above, with the conventional method and apparatus, in order to comprehend the progress of the removal of excessive water from the blood and also to monitor as to whether the water removal is properly taking place, the amount of water removed has to be metered occasionally during the dialysis. According to the prior art, the measurement of the amount of water removed is carried out in the following manner: Two pumps of equal volume are connected mechanically and inserted respectively in a solution supply piping leading to the solution inlet 8a and in a dialysate discharge piping leading from the dialysate outlet 8b. While the dialyzing solution is supplied through the dialysate chamber at a rate of about 500 ml/min. continously, the flow of about 10 ml/min. is forcibly discharged by the use of a water removal pump of small volume fluid-connected with the dialysate discharge piping through a branch piping to effect a forced water removal in equal quantity. The amount of the water removed is measured in terms of the amount discharged from the water removal pump.
However, with this prior art method, it has been found that the apparatus required to measure the amount of the water removed tends to become complicated and bulky, and since a constant quantity of water is forcibly removed, the patient being dialyzed must be carefully watched for the purpose of safety.
Another prior art method for the measurement of the water removal comprises interrupting the supply of the dialyzing solution for a few minutes per hour, measuring both the amount of water removed during the interruption of the supply of the dialyzing solution for the purpose of sampling and the conditions in which the water removel during the interruption of the supply of the dialyzing solution takes place, and controlling the water removal condition during the normal dialyzing operation on the basis of the result of the measurement so that the total amount of the water removed can be deduced. However, according to this alternative prior art method, the control of the water removal condition is not always easy and the total amount of the water removed is nothing other than the deduced value. Therefore, this alternative prior art method has a disadvantage in that a highly accurate measurement is impossible and, if the accurate measurement were to be achieved, it does not mean that such accurate measurement can be achieved at all times.
In view of the foregoing, the prior art methods for the measurement of the water removed requre the continuous supply of the dialyzing solution through the dialysate chamber of the dialyzer unit so that the whole, or substantially whole, process of dialysis can be performed during the measurement. This is hitherto considered as an essential requirement for the dialysis to be performed and, accordingly, this requirement renders it difficult to perform the measurement of the water removed.